This application claims the priority benefit of Taiwan application serial no. 89123186, filed Nov. 3, 2000.
1. Field of the Invention
The invention relates in general to a method of forming silicon carbide. More particularly, this invention relates to a method of properly stripping the silicon carbide formed over a silicon wafer used as a dummy wafer to inspect the properties of the silicon carbide, so that the silicon wafer can be recycled without performing additional processes such as polishing and re-growth.
2. Description of the Related Art
In a conventional integrated circuit, a dielectric layer with a high dielectric constant (referred as a high k dielectric layer hereinafter) such as silicon nitride with k=7.0 is often used as a barrier layer for preventing diffusion between copper (Cu) and low k dielectric layers while forming copper line. Alternatively, this kind of dielectric layer is also frequently applied as a stop layer for the low k dielectric layer. However, the high k dielectric layer causes a high RC delay since it induces a high parasitic capacitance. As the integrated circuit becomes more and more condense and the process line width thereof shrinks, the RC delay affects the device performance more and more seriously.
To solve the above problem, the silicon carbide material with a lower dielectric constant (k less than 5) is used. Before the practical application, a silicon carbide layer is formed on a silicon wafer which is used as a dummy wafer. After the property inspection of such silicon carbide layer, it is expected that the silicon carbide can be stripped and the silicon wafer can be recycled. However, due to the hydrophobia of the silicon carbide surface, the wetting effect of acid or alkaline solution is too poor to strip the silicon carbide from the silicon wafer. Moreover, the chemical bonding of high carbon content of silicon carbide makes it even more difficult for removal. Therefore, after property inspection, the whole silicon wafer has to be polished in the supplying manufacture for recycle. Otherwise, the silicon wafer used as the dummy wafer has to be abandoned.
If the silicon carbide is formed on a base layer of silicon oxide or silicon nitride, the silicon carbide can be stripped using acid solution to remove the base layer. However, this kind of process cannot be continuously operated. In addition, the stripped silicon carbide is easily to block the filter of such acid solution to damage the acid circulation of the machine. If one uses dry etch to strip the silicon carbide, it is easily to cause carbon containing polymer adhered on the silicon wafer. In this case, an additional treatment is required to complicate the stripping process, so that the recycle cost is increased.
The invention provides a method of removing silicon carbide. A silicon wafer is used as a dummy wafer for inspecting the properties of a silicon carbide thin film which is to be formed thereover. A silicon nitride layer with a thickness larger than about 1000 angstroms is formed on the dummy wafer as a base layer of the silicon carbide thin film. The silicon carbide thin film is then formed on the base layer. The property inspection of the silicon carbide thin film is performed. After the properties inspection, the silicon carbide is stripped using a high density hydrogen plasma. After the step of high density hydrogen plasma, if the remaining silicon nitride layer is thicker than about 500 angstroms, the remaining silicon nitride layer can be used as the base layer again for forming and inspecting the properties of the silicon carbide thin film. In contrast, if the remaining silicon nitride layer is thinner than about 500 angstroms, an acid solution is used to dip and remove the remaining silicon nitride layer, and the silicon wafer can then be recycled.
In the above method, both the silicon nitride layer and the silicon carbide thin film are preferably formed by plasma enhanced chemical vapor deposition (PECVD). The content of the silicon carbide preferably includes 20-35% of carbon atoms, 20-40% of silicon atom, 20-50% of hydrogen atoms and 0-10% of nitrogen atoms. The condition for the high density hydrogen plasma preferably includes a temperature of about 350-450xc2x0 C. in the reaction chamber, a pressure of about 4-8 mTorr, a hydrogen flow rate of about 300-800 sccm and a low frequency RF power of about 3000-4000 W at about 1 MHz. The duration for the high density hydrogen plasma is about 1-3 minutes plus the time for forming the silicon carbide thin film.
In the method mentioned above, the silicon wafer or the base layer and the silicon wafer can be recycled without causing the problems occurring in the conventional method. The fabrication cost can thus be greatly reduced.
Both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.